#
# 10a
#
import math


def main():
    x1, y1, x2, y2 = map(float, input().split())
    ret = math.sqrt(pow(x1-x2, 2) + pow(y1-y2, 2))
    print(f"{ret: .8f}")


if __name__ == '__main__':
    main()
 import math math def main():
    x1, y1, x2, y2 = map(float, input().split())
    ret = math.sqrt(pow(x1-x2, 2) + pow(y1-y2, 2))
    print(f"{ret: .8f}") main x1, y1, x2, y2 = map(float, input().split()) x1 map(float, input().split()) map float input().split() ().split () input split y1 x2 y2 ret = math.sqrt(pow(x1-x2, 2) + pow(y1-y2, 2)) ret math.sqrt(pow(x1-x2, 2) + pow(y1-y2, 2)) math.sqrt math sqrt pow(x1-x2, 2) + pow(y1-y2, 2) pow(x1-x2, 2) pow x1-x2 x1 x2 2 pow(y1-y2, 2) pow y1-y2 y1 y2 2 print(f"{ret: .8f}") print f"{ret: .8f}" if __name__ == '__main__':
    main() __name__ == '__main__' __name__ '__main__' main() main def main():
    x1, y1, x2, y2 = map(float, input().split())
    ret = math.sqrt(pow(x1-x2, 2) + pow(y1-y2, 2))
    print(f"{ret: .8f}") def main():
    x1, y1, x2, y2 = map(float, input().split())
    ret = math.sqrt(pow(x1-x2, 2) + pow(y1-y2, 2))
    print(f"{ret: .8f}") main
#
# 10a
#
import math


def main():
    x1, y1, x2, y2 = map(float, input().split())
    ret = math.sqrt(pow(x1-x2, 2) + pow(y1-y2, 2))
    print(f"{ret: .8f}")


if __name__ == '__main__':
    main()

